The present disclosure relates to focus metrology.
A photolithography system is a machine that applies a pattern onto a substrate, usually onto a target portion of the substrate. A photolithography system can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a mask or a reticle may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion of a substrate. Transfer of the pattern is typically via imaging onto a resist provided on the substrate.
During the operation of the photolithography system, a plurality of parameters of an operation recipe for the photolithography system should be determined base on the surface of the substrate. The focal length is one of them. If the focal length is incorrectly determined, the pattern imaged onto the resist will be out of focus and thus blurred.